A vehicle is generally equipped with a radiator to improve cooling efficiency of a coolant for cooling the engine of the vehicle, and a cooling fan to blow air to the radiator to cool the coolant passing through the radiator is installed around the radiator. The cooling fan is connected with a fluid fan clutch, which receives power transferred via a water pump pulley of the engine and transfers the power to the cooling fan to rotate the cooling fan when the temperature of the radiator is high.
Hereinafter, a conventional fluid fan clutch will be described in detail with reference to an accompanying drawing.
FIG. 1 is a cross-sectional view schematically illustrating configuration of a typical fluid fan clutch according to conventional art.
As shown in FIG. 1, a typical fan clutch includes a fan housing 10 including a housing body 11 and a housing cover 12, which are detachably coupled to each other. A rotor 40 is rotatably installed in the inner space of the fan housing 10. The rotor 40 is integrally coupled to a rotor shaft 20, which is rotated by rotational force transferred from the engine crankshaft (not shown), such that the rotor 40 can rotate together with the rotor shaft 20. Herein, a bearing 30 is interposed between the fan housing 10 and the rotor shaft 20. When the rotor shaft 20 rotates, the fan housing 10 is not directly caused to rotate at the same time.
The inner space of the fan housing 10 is divided into a fluid storage chamber S and a fluid operation chamber D by a separation plate 50, as shown in FIG. 1. A working fluid is stored in the fluid storage chamber S, and the rotor 40 is disposed in the fluid operation chamber D. Meanwhile, a supply valve 60 operating to allow the working fluid to be supplied from the fluid storage chamber S to the fluid operation chamber D is installed on one side of the separation plate 50. The supply valve 60 is generally driven by an actuator 61 employing a bimetal element, as shown in FIG. 1.
According to this structure, as the rotor shaft 20 rotates, the rotor 40 rotates in the fluid operation chamber D of the fan housing 10 with the fan housing 10 remaining stationary. When the supply valve 60 opens, the working fluid flows from the fluid storage chamber S into the fluid operation chamber D. Thereby, the fan housing 10 rotates along with the rotor 40 in the fluid operation chamber D due to viscous resistance of the working fluid. As the viscous resistance increases with increase in the amount of the supplied working fluid, slips with respect to rotation of the rotor 40 are reduced, and the rotational speed of the fan housing 10 increases.
The working fluid supplied from the fluid storage chamber S to the fluid operation chamber D is moved outward within the fluid operation chamber D by centrifugal force according to rotation of the rotor 40, circulated along a return flow path 70 formed inside the fan housing 10 and then collected in the fluid storage chamber S, as shown in FIG. 1. As the collected working fluid continues to circulate from the fluid storage chamber S to the fluid operation chamber D in this way, the rotor 40 and the fan housing 10 rotate.
The supply valve 60 is driven by the actuator 61 employing a bimetal element, as shown in FIG. 1. Specifically, the bimetal element is configured to change according to the temperature of a coolant contained the radiator. Thereby, the actuator 61 causes the supply valve 60 to open when the temperature of the coolant is high and to close when the temperature of the coolant is low. Therefore, the fluid fun clutch is configured to properly operate according to the coolant temperature in a manner that the fan housing 10 is rotated or stopped by opening and closing of the supply valve 60 performed according to the coolant temperature.
For the conventional fluid fan clutch configured as above, however, flow of the fluid from the storage chamber S into the operation chamber D is controlled by the supply valve 60, while flow of the fluid from the operation chamber D into the storage chamber S is caused by centrifugal force of the rotor 40. Accordingly, return of the fluid cannot be artificially controlled. That is, since the fluid flows from the operation chamber D back to the storage chamber S along the return flow path 70 while the fluid is being supplied to the operation chamber D, it takes a long time to fill the operation chamber D with the fluid.
Of course, if a separate valve is added to shut the return flow path 70, flow of the fluid from the operation chamber D to the storage chamber S may be controlled. However, adding the separate valve may result in a very complex internal structure of the fan housing 10 and need a separate signal input for control of the valve, thereby making it difficult to manipulate the fluid fan clutch.